This invention relates to a hydraulic jack of the type which is operated manually.
Various proposals have been heretofore made in connection with an hydraulic jack set of the manually-operated type. In principle, as shown in FIG. 4, the jack comprises an oil pressure supply and discharge part 1 and a jack part 2. The oil pressure supply and discharge part 1 converts unpressurized oil from a tank 13 into pressure oil by means of an oscillating operation of an operating lever 11 with respect to a pump 12, and supplies the oil to the jack part 2 through a pipe 3. On the other hand, oil from the jack part 2 is returned to the tank 13 by an opening a depressurizing valve 14. It is set so that the jack part 2 extends when pressure oil from the oil pressure supply and discharge part 1 is supplied, and the jack part 2 contracts when pressure oil is discharged.
Accordingly, in the conventional hydraulic jack, for example, the jack part 2 is located at a desired position for extension and contraction thereof to enable movement of heavy articles up and down. Further, where the jack part 2 is a pantograph type, it is possible to set an elevating stroke higher than when the jack part 2 is a cylinder type.
However, when the jack part 2 is a pantograph type, the elevating stroke is large, and therefore, it is necessary to stabilize the jack when the jack is placed on the installing surface such as the surface of the earth. For example, though not shown, a base plate or the like constituting the lower end of the jack part 2 is formed as large as possible.
On the other hand, when the hydraulic jack of this kind is located at a deep position, in most case, the operating lever 11 included in the oil pressure supply and discharge part 1 is used as a pressing/positioning member by which the jack part 2 is slidably moved and fed into the desired position.
In this case, the larger the base plate or the like constituting the lower end of the jack part 2, which enhances the stability when installed, as described above, here poses an inconvenience in that the feeding operation is difficult.
This invention has been designed in view of the aforementioned circumstances. An object of the invention is to provide a hydraulic jack in which feeding/positioning a jack part into a desired position is optimized for a wide use of the jack in different applications.
For achieving the aforesaid object, a means of the present invention comprises an oil pressure supply and discharge part, and a jack part connected to the oil pressure supply and discharge part through a flow passage. The jack part is provided with a hydraulic cylinder, a pantograph type link connected to the hydraulic cylinder through a driving link, and a wheel provided at a suitable position of the pantograph type link.
In this case, preferably, the pantograph type link comprises a pair of rotatable lower links, a pair of upper links pivotally mounted on extreme ends of the lower links, respectively, through shafts, and pressure receiving plates provided on the upper ends of the upper links, respectively, the driving link is connected rotatably between the hydraulic cylinder and the lower links, and the wheel is mounted on one of the shafts.
In this case, preferably, the lower links and the upper links are provided in a paired relation before and behind the hydraulic cylinder, and the wheel is mounted on the front shaft for pivotally mounting the front lower link and the front upper link.
Further, in the above-described means, preferably, a guide tube comprising an outer tube, and an inner tube slidably inserted into the outer tube, is connected to the jack part. The oil pressure supply and discharge part is provided with a holder member, the pipe is inserted into the guide tube, and the guide tube is connected to the holder member reparably and rotatably.
In this case, preferably, an operating rod extending in a direction opposite to the guide tube is connected to the holder member.
Further, preferably, the jack part has a base plate movably placed on the installing surface, and the base plate is connected to the inner tube through a connecting construction.
Furthermore, preferably, the oil pressure supply and discharge part has a pump and a tank. The tank comprising a bellows type bladder for setting a volume chamber therein, and a protective casing formed of a visible material for receiving the bladder therein.